Integrated Circuits and Systems group, IIT Madras

Charge pump -ve voltage generator

  • Goals:
    • Design a negative voltage generator from a positive supply.
    • Design a circuit to get a higher voltage than the available supply

  • Analyze the circuit in the figure above. Determine the waveforms VA and VB in steady state

  • Transistors Mn1 and Mn2 are added to multiplex VA and VB and result in Vout. Implement this circuit using CD4069 inverters. Think carefully about which terminal goes where! You'll need to use separate ICs for the inverter and the rest of the circuitry because, on a chip, the supply and ground pins are all shorted together. You can use clock frequencies in the tens of kHz range, capacitors in the 10nF range, and a supply of 5V.
  • What is the output voltage Vout with no load(CL)? and with a constant current load IL?
  • Build and demonstrate a circuit that gives a positive output of approximately twice the power supply wrt ground.
  • Applications: This is useful when a dual supply is required to be generated from a single supply, such as a battery. Such circuits are used in audio amplifiers which, when operated from a dual supply, have a quiescent output of 0V and hence don't need a bulky ac coupling capacitor. These circuits are also used when a small portion of the IC needs a higher supply voltage, but multiple power supplies can't be used. Examples are flash memories(USB sticks) and EEPROMS which operate from a low voltage supply(3V-5V in a mobile phone/MP3 player) but need a high voltage(~ 15V) for write/erase.